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Abstract N ‐alkylation of 5‐hydroxynicotinic acid esters with electrophiles containing diene functionality produces salts that undergo intramolecular (4+3) cycloaddition reactions upon heating in the presence of base. Initial studies used a three‐carbon tether to join the pyridinium ion and diene, revealing some aspects of the inherent selectivity of the reaction with such substrates. Much more challenging was the synthesis of related species possessing only a two‐carbon tether. Nevertheless, the cycloaddition of such compounds was successful, leading directly to the ABC ring system of the alkaloid daphnicyclidin A. -
This account describes how I began my adventure in the area of (4+3)-cycloadditions and then focuses on two ongoing projects: a new catalytic asymmetric (4+3)-cycloaddition and what might be described as the ‘rebirth’ of oxidopyridinium ion (4+3)-cycloaddition chemistry. References to other people’s work are made where appropriate. 1 Introduction 2 Asymmetric, Catalytic (4+3)-Cycloadditions 3 Oxidopyridinium Ions and (4+3)-Cycloadditions 4 Conclusions and the Futuremore » « less
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Abstract N ‐Methylation of methyl 5‐hydroxynicotinate followed by reaction with a diene in the presence of triethylamine afforded (4+3) cycloadducts in good to excellent yields. High regioselectivity was observed with 1‐substituted and 1,2‐disubstituted butadienes. Density functional theory calculations indicate that the cycloaddition involves concerted addition of the diene onto the oxidopyridinium ion. The process provides rapid access to bicyclic nitrogenous structures resembling natural alkaloids. -
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Abstract N ‐Methylation of methyl 5‐hydroxynicotinate followed by reaction with a diene in the presence of triethylamine afforded (4+3) cycloadducts in good to excellent yields. High regioselectivity was observed with 1‐substituted and 1,2‐disubstituted butadienes. Density functional theory calculations indicate that the cycloaddition involves concerted addition of the diene onto the oxidopyridinium ion. The process provides rapid access to bicyclic nitrogenous structures resembling natural alkaloids.
